As a process of forming an electronic circuit, a process using a photosensitive resin composition is generally employed.
In the process of forming a circuit using a photosensitive resin composition, through a step of forming a resist film composed of a photosensitive resin composition on the surface of the substrate, a step of irradiating the light to the resist film through a mask to form a latent image, a step of developing the resist film in which a latent image was formed, using a developing solution to form a resist pattern, and a step of chemically etching and plating a part where the resist is not presented, then the electronic circuit is formed.
In addition, in the chip-on-film (COF) in which a bare chip was directly arranged on the flexible substrate and the multilayer printed wiring board obtained by the build-up method, the miniaturization of electronic circuits has been investigated. In the circuit formation process for the COF and the multilayer printed wiring board obtained by the build-up method, at the step corresponding to the normal development step in the printed wiring board, 1% by weight aqueous solution of sodium carbonate is used as a developing solution.
As the conventional photosensitive resin composition, the following is known.
(1) Photosensitive resin composition containing a compound consisting of a novolac resin, a quinonediazide compound, cyclohexanes, and phenols (Patent Document 1).
(2) Photosensitive resin composition containing a vinyl-based polymer having a structural unit derived from a monomer having a phenolic hydroxyl group and a structural unit derived from a vinyl-based monomer containing a carboxyl group, and a quinonediazide compound (Patent Document 2).
(3) Photosensitive resin composition containing a vinyl-based copolymer having a structural unit derived from a vinyl-based monomer containing a carboxyl group, a quinonediazide compound, and a polyhydric phenol compound (Patent Document 3).
However, a novolac resin contained in the photosensitive resin composition of (1) is a brittle resin, and if the photosensitive resin composition containing a novolac resin is used as a resist film, there is a problem that cracks are likely to occur onto the resist film. In particular, if the photosensitive resin composition is made into a dry film, because the dry film is wound, the aforementioned problem becomes noticeable.
In addition, because the solubility of the photosensitive resin composition (2) in an aqueous solution of sodium carbonate is bad, when the photosensitive resin composition (2) is used in circuit formation process in the COF and the multilayer printed wiring board obtained by the build-up method, the resolution is likely to be insufficient. Further, if the monomer component having a phenolic hydroxyl group is polymerized, the resulting vinyl-based polymer has a relatively low molecular weight. Therefore, making a vinyl-based polymer with a high molecular weight is difficult. For this reason, plating resistance of the resist film becomes insufficient.
In addition, in the photosensitive resin composition of (3), because the vinyl-based copolymer does not have a phenolic hydroxyl group, there is no interaction between the phenolic hydroxyl group and a quinonediazide. Therefore, the unexposed area of the resist film is easily dissolved, and is likely to occur the film reduction.
From the background described above, in the circuit formation process in the COF and the multilayer printed wiring board obtained by the build-up method, a photosensitive resin composition which can form a resist film in which the occurrence of cracks is suppressed, the film reduction of an unexposed area is suppressed, sensitivity and resolution are excellent, and the plating resistance is superior.